Hydrocarbons, such as oil and gas, may be recovered from various types of subsurface geological formations. The formations typically consist of a porous layer, such as limestone and sands, overlaid by a nonporous layer. Hydrocarbons cannot rise through the nonporous layer, and thus, the porous layer forms a reservoir in which hydrocarbons are able to collect. A well is drilled through the earth until the hydrocarbon bearing formation is reached. Hydrocarbons then are able to flow from the porous formation into the well.
In what is perhaps the most basic form of rotary drilling methods, a drill bit is attached to a series of pipe sections referred to as a drill string. The drill string is suspended from a derrick and rotated by a motor in the derrick. A drilling fluid or “mud” is pumped down the drill string, through the bit, and into the wellbore. This fluid serves to lubricate the bit and carry cuttings from the drilling process back to the surface. As the drilling progresses downward, the drill string is extended by adding more pipe sections. When the drill bit has reached the desired depth, larger diameter pipes, or casings, are placed in the well and cemented in place to prevent the sides of the borehole from caving in. Cement is introduced through a work string. As it flows out the bottom of the work string, fluids already in the well, so-called “returns,” are displaced up the annulus between the casing and the borehole and are collected at the surface.
Once the casing is cemented in place, it is perforated at the level of the oil bearing formation so oil can enter the cased well. If necessary, various completion processes are performed to enhance the ultimate flow of oil from the formation. The drill string is withdrawn and replaced with a production string. Valves and other production equipment are installed in the well so that the hydrocarbons may flow in a controlled manner from the formation, into the cased well bore, and through the production string up to the surface for storage or transport.
This simplified drilling process, however, is rarely possible in the real world. For various reasons, a modern oil well will have not only a casing extending from the surface, but also one or more pipes, i.e., casings, of smaller diameter running through all or a part of the casing. When those “casings” do not extend all the way to the surface, but instead are mounted in another casing, they are referred to as “liners.” Regardless of the terminology, however, in essence the modern oil well typically includes a number of tubes wholly or partially within other tubes.
Thus, many wells today are drilled in stages. An initial section is drilled, cased, and cemented. Drilling then proceeds and a liner is run into the uncased portion of the well and installed. More specifically, the liner is suspended from the original casing by an anchor or “hanger.” A seal also is typically established between the liner and the casing and, like the original casing, the liner is cemented in the well. That process then may be repeated to further extend the well and install additional liners.
Conventional liner anchors or “hangers” have included various forms of mechanical slip mechanisms that are connected to the liner. The slips themselves typically are in the form of cones or wedges having teeth or roughened surfaces. An installation tool is used to position the anchor in place and drive the slips from their initial, unset position, into a set position where they are able to bite into and engage the existing casing. The setting mechanisms typically are either hydraulic, which are actuated by increasing the hydraulic pressure within the tool, or mechanical, which are actuated by rotating, lifting, or lowering the tool, or some combination thereof. Those types of mechanical hangers typically require a separate annular seal or “packer” in order to seal the liner to the casing.
One approach to avoiding the need for separate packers and other problems attendant to mechanical hangers has been to eliminate in a sense the anchor entirely. That is, instead of using a separate anchor assembly, a portion of the liner itself is expanded into contact with an existing casing, making the liner essentially self-supporting and self-sealing. Such expandable liners, also commonly referred to as expandable hangers and expandable liner hangers, are made of sufficiently ductile metal to allow radial expansion of the liner, or more commonly, a portion of the liner into contact with existing casing. Various mechanisms, both hydraulic and mechanical, are used to expand the liner. Such approaches, however, all rely on direct engagement of, and sealing between the expanded liner and the existing casing.
For example, U.S. Pat. No. 7,225,880 to B. Braddick discloses an expandable liner. The liner is set within the casing by actuating an expander that radially expands the upper portion of the liner into engagement with a casing. Once expanded, the expanded portion of the liner provides a seal that prevent fluids from flowing between the liner and casing. The tubular expander is not withdrawn from the liner after the expandable portions have been expanded. It is designed to remain in the liner and provide radial support for the expanded liner.
U.S. Pat. No. 7,387,169 to S. Harrell et al. also discloses various methods of hanging liners and tying in production tubes by expanding a portion of the tubular via, e.g., a rotating expander tool. All such methods rely on creating direct contact and seals between the expanded portion of the tubular and the existing casing.
Such approaches have an advantage over traditional mechanical hangers. The external surface of the liner has no projecting parts and generally may be run through existing conduit more reliably than mechanical liner hangers. Moreover, the expanded liner portion not only provides an anchor for the rest of the liner, but it also creates a seal between the liner and the existing casing, thus reducing the need for a separate packer. Nevertheless, they suffer from significant drawbacks.
First, because part of it must be expandable, the liner necessarily is fabricated from relatively ductile metals. Such metals typically have lower yield strengths, thus limiting the amount of weight and, thereby, the length of liner that may be supported in the existing casing. Shorter liner lengths, in deeper wells, may require the installation of more liner sections, and thus, significantly greater installation costs. This problem is only exacerbated by the fact that expansion creates a weakened area between the expanded portion and the unexpanded portion of the liner. This weakened area is a potential failure area which can damage the integrity of the liner.
Second, it generally is necessary to expand the liner over a relatively long portion in order to generate the necessary grip on the existing casing. Because it must be fabricated from relatively ductile metal, once expanded, the liner portion tends to relax to a greater degree than if the liner were made of harder metal. This may be acceptable when the load to be supported is relatively small, such as a short patch section. It can be a significant limiting factor, however, when the expanded liner portion is intended to support long, heavy liners.
Thus, some approaches, such as those exemplified by Braddick '880, utilize expanders that are left in the liner to provide radial support for the expanded portion of the liner. Such designs do offer some benefits, but the length of liner which must be expanded still can be substantial, especially as the weight of the liner string is increased. As the length of the area to be expanded increases the forces required to complete the expansion generally increase as well. Thus, there is progressively more friction between the expanding tool and the liner being expanded and more setting force is required to overcome that increasing friction. The need for greater setting forces over longer travel paths also can increase the chances that liner will not be completely set.
Moreover, the liner necessarily must have an external diameter smaller than the internal diameter of the casing into which it will be inserted. This clearance, especially for deep wells where a number of progressively smaller liners will be hung, preferably is as small as possible so as to allow the greatest internal diameter for the liner. Nevertheless, if the tool is to be passed reliably through existing casing, this clearance is still relatively large, and therefore, the liner portion is expanded to a significant degree.
Thus, it may not be possible to fabricate the liner from more corrosion resistant alloys. Such alloys typically are harder and less ductile. In general, they may not be expanded, or expanded only with much higher force, to a degree sufficient to close the gap and grip the existing casing.
Apart from, and partially because of those shortcomings, expandable liners also create tradeoffs in cementing the liner. Because they establish a seal between the liner and existing casing, once an expandable liner is fully set fluids displaced up the annulus as cement is injected, the so-called “returns,” can no longer flow around the liner on their way to the surface. Thus, some expandable liners, such as those disclosed in Braddick '880, are not set until after cementing has been completed.
Other expandable liners partially expand the liner in such a way as to leave vertical return flow paths between the liner and casing. For example, U.S. Pat. No. 7,441,606 to P. Maguire, U.S. Pat. No. 7,048,065 to R. Badrak et al., and U.S. Pat. No. 6,598,677 to J. Baugh disclose expandable liners which are expanded in two stages. In the first stage, the liner is partially expanded so as to engage a casing wall, but not completely seal the annulus around the liner. Vertical flow paths are left to allow returns from a cementing operation to flow around the liner to the casing above. After cementing is complete, the liner is fully expanded around its entire circumference and a separate annular seal is set.
Other expandable liners, such as liners disclosed in Baugh '677, are partially expanded to create an initial seal before cementing. A flow path for returns is created by providing a port in the expandable liner and passageways through the swage which is used to expand the liner. The swage remains engaged with the liner, and returns entering the liner through the port flow through the passageways in the swage. When the cementing operation is concluded, the swage is actuated to finish expanding the liner, including the area around the port, thus sealing off the port.
Baugh '677 also discloses a similar hanger where, instead of sealing the port by expanding the liner around it, a slidable cover is provided on the exterior of the liner. The cover is actuated to shut the port after cementing has been completed, but there is no disclosure of any mechanism or method of doing so. In any event, the swage remains engaged with the liner and is not withdrawn until after cementing is complete and the port is shut.
All of those approaches suffer from a common deficiency. That is, the swage or other mechanisms by which the liner is expanded and the hanger is set and sealed are not disengaged until after cementing has been completed. In most instances, setting and sealing of the liner also is not completed until after the liner is cemented. Cementing the liner before it has been fully set, however, has its own set of problems. Most significantly, it means that the liner will be cemented in place before an operator knows that the setting mechanism has operated properly, that an effective seal has been established with existing casing, and that he is able to retrieve the tools used to install the liner. Any difficulties in those operations usually are more easily overcome if the liner has not been cemented.
Moreover, even where it is possible to establish a seal, the manner in which flow paths for returns are established in conventional expandable liners leaves much to be desired. The fabrication and assembly of the installation tool is unnecessarily complicated by any need to provide passages in the swage or other tool components. Moreover, because they are made from relatively ductile metals, expandable liners already suffer from various weak points and potential failure areas as discussed above. Providing ports through an expandable liner exacerbates that problem.
Another reality facing the oil and gas industry is that most of the known shallow reservoirs have been drilled and are rapidly being depleted. Thus, it has become necessary to drill deeper and deeper wells to access new reserves. Many operations, such as installing a liner, can be practiced with some degree of error at relatively shallow depths. Similarly, the cost of equipment failure is relatively cheap when the equipment is only a few thousand feet from the surface.
When the well is designed to be 40,000 feet or even deeper, such failures can be costly in both time and expense. Apart from capital expenses for equipment, operating costs for modern offshore rigs can be $500,000 or more a day. There is a certain irony too in the fact that failures are not only more costly at depth, but that avoiding such failures is also more difficult. Temperature and pressure conditions at great depths can be extreme, thus compounding the problem of designing and building tools that can be installed and will function reliably and predictably.
The increasing depth of oil wells also means that the load capacity of a connection between an existing casing and a liner, whether achieved through mechanical liner hangers or expanded liners, is increasingly important. Higher load capacities may mean that the same depth may be reached with fewer liners. Because operational costs of running a drilling rig can be so high, significant cost savings may be achieved if the time spent running in an extra liner can be avoided.
Ever increasing operational costs of drilling rigs also has made it increasingly important to combine operations so as to reduce the number of trips into and out of a well. For example, especially for deep wells, significant savings may be achieved by drilling and lining a new section of the well at the same time. Thus, tools for setting liners have been devised which will transmit torque from a work string to a liner. A drill bit is attached to the end of the liner, and the liner is rotated.
Such disadvantages and others inherent in the prior art are addressed by the subject invention, which now will be described in the following detailed description and the appended drawings.